class Circle:
    PI = 3.1415926   #类属性  用类名去调用 Circle.PI
    def __init__(self):
        self.radius = 0
         #初始化的方法

    def area(self):
        self.c_area = self.radius * self.radius * Circle.PI
        print('圆的面积为：',self.c_area)

    def perimeter(self):
        self.pe = self.radius *2 * Circle.PI
        print('圆的周长为：',self.pe)

    def input_radius(self):
        self.radius = float(input('请输入圆的半径：'))

c1 = Circle()
# c1.input_radius()
Circle.PI = 314
print (Circle.PI)
c1.radius = 2.5
print (c1.radius)
# c1.area()
# c1.perimeter()